Spin torque transfer technology, also referred to as spin electronics, which is based on changing magnetic state of the system by momentum transfer from conduction electrons, is a recent development. Spin torque RAM or ST RAM is a non-volatile random access memory application that utilizes spin torque technology. Digital information or data, represented as a “0” or “1”, is storable in the alignment of magnetic moments within a magnetic element. The resistance of the magnetic element depends on the moment's alignment or orientation. The stored state is read from the element by detecting the component's resistive state.
The magnetic element, in general, includes a ferromagnetic pinned layer (PL), and a ferromagnetic free layer (FL), each having a magnetization orientation. The magnetic element also includes a non-magnetic barrier layer. The respective magnetization orientations of the free layer and the pinned layer define the resistance of the overall magnetic element. When the magnetization orientations of the free layer and pinned layer are parallel, the resistance of the element is low (RL). When the magnetization orientations of the free layer and the pinned layer are antiparallel, the resistance of the element is high (RH). The magnetization orientation is switched by passing a current perpendicularly through the layers. The current direction is different for writing “1” or ‘0”. To write “1” (RH) the current flows from the pinned layer to the free layer, and reversed to flow from the free layer to the pinned layer to write “0” (RL).
It is desirous to reduce the switching current needed to switch the free layer magnetization orientation, since larger chip capacity and/or reduced power consumption is achieved.